CN1146006C - Shadow mask for color picture tube - Google Patents

Abstract

The present invention relates to a shadow mask for a color cathode ray tube. The present invention aims to largely avoid the arching phenomenon of the shadow mask caused by the action of electron beams, using low-cost steel as the material for the shadow mask. The shadow mask of the present invention is characterized in that the cathode-side surface of the shadow mask comprises at least one thermal insulation layer and at least one covering layer containing a heavy metal. The thermal insulation layer is located between the shadow mask and the covering layer and is composed of thermally stable porous solid particles. Each layer has a binder.

Description

Shadow mask for color picture tube

technical field

The invention relates to a shadow mask for a color picture tube, which is mainly composed of iron metal, the mask is fixed with a frame, and is arranged in front of a fluorescent screen formed, the cathode side surface of the shadow mask has at least one heat insulating layer and at least one layer A covering layer containing heavy metal, the heat insulating layer is disposed between the shadow mask and the covering layer.

Background technique

In color picture tubes with a shadow mask, the mask is arranged directly adjacent to the inner surface of the phosphor screen. Since each light-emitting area is formed on the inner surface of the fluorescent screen, the geometric dimensions of the shadow mask are required to be consistent with the configuration of the light-emitting area when the color picture tube is in operation. Maximum impingement precision of the electron beams on the luminescent regions can be achieved when the geometry of the apertures in the shadow mask corresponds to the distribution of the luminescent regions on the inner surface of the phosphor screen at operating temperature. However, since only a small fraction of the emitted electrons pass through the shield and hit the light-emitting region and most of the electrons hit the shield directly, the shield is heated up to 80°C. This results in a change in the housing geometry, which in turn causes the housing to arch (arching effect).

The aperture geometry of the shadow mask no longer coincides with the respective light-emitting area pattern. This results in inaccurate impacts of the electrons. Decreases the color reproduction quality of the fluorescent screen.

For high contrast images, different regions of the mask will be heated to different degrees, thus causing partial arching of the mask (partial arching) and image distortion when allowed tolerances are exceeded.

Various attempts have been made to limit or prevent this detrimental thermal condition of the shadow mask. Therefore, various measures have been established to limit the overheating of the enclosure.

U.S. Patent No. 3887 828 proposes disposing a porous manganese dioxide layer on a metallic shadow mask (Lochmaske) and disposing a thin layer of metallic aluminum on its top surface. The metal aluminum layer is in contact with the shadow mask only at the edge of the aperture. It should be electrically conductive and electron absorbing. Over the aluminum layer is another layer of graphite, nickel oxide or nickel iron.

The porosity proposed therein for the manganese oxide layer is believed to be primarily due to the individually distributed particles, which form a sandwich-like structure with the thin aluminum layer. Due to the structure of this layer, the heat generated by the electron impact will be away from the metal shadow mask and radiated in the opposite direction.

This solution has various disadvantages. It has been shown that keeping the heat generated away from the porous mask has not proven feasible since most of the heat is not generated in the aluminum and overlapping graphite layers but in the shadow mask. The electron reflectivity, electron absorption and heat dissipation properties of the aluminum layer are too low. An insulating sandwich disposed on the shadow mask has the opposite effect: heat may be difficult to dissipate.

An electronic reflective layer applied directly on the shadow mask is described in DE 3125075 C ₂ . This layer contains heavy metals, especially their carbides, sulfides or oxides. Up to 30% of the electrons may be reflected when the electron beam strikes, which means that the shadow mask is less heated. However, most of the electrons still reach the mask, causing undesired heating therein, and thus general and local cambering of the mask.

US Patent No. 4671776 proposes to use borate glass to coat the shadow mask. Glass powder is sputtered onto the shield and then melted. The glass layer is very firmly bonded to the substrate. In operation, the arching effect is eliminated due to some insulation but mostly due to tension within the mask caused by the different coefficients of expansion of the metal and coating in the mask. With this coating, it is difficult to observe the electron reflection effect, where a large part of the impact energy of the electron beam is still transmitted to the shield, resulting in an unfavorable arching condition.

Furthermore, a rigid fixing of the cover with a stable glass layer can no longer meet the higher requirements for color image quality in the multimedia era.

Another way to significantly limit the undesirable doming phenomenon is to use high quality metal alloys such as Invar for the shadow mask, since this alloy has a particularly favorable coefficient of thermal expansion. However, this material is too expensive.

However, since the cost share of the shadow mask in the overall cost of the color picture tube is already relatively high, the use of special metal alloys will lead to a further increase in costs.

Contents of the invention

The object of the present invention is to largely avoid arching of the shadow mask due to the action of electron beams by using low-cost steel as the mask material.

Solutions to this problem include: the insulation layer is composed of thermally stable porous solid particles, and each layer contains a binder.

According to the present invention, a heat insulating layer is formed on the cathode side surface of the shadow mask, and electron reflecting, electron absorbing, and heat radiating layers are coated on said layer. Some electrons are thus reflected, while others are absorbed in the covering layer and converted into heat, wherein due to the configuration of the insulating layer according to the invention the heat does not act directly on the shadow mask but radiates to the inside of the tube. Local temperature differences leading to local cambering of the shadow mask are thereby also eliminated. Such local temperature differences occur especially for high-contrast images.

The insulating layer consists of heat-resistant porous solid particles embedded in a binder. According to the present invention, the porous solid particles may be various oxide, sulfide, silicate and/or aluminophosphate materials or mixtures of materials. Among them, silicic acid, zirconium dioxide and titanium dioxide are suitable porous materials as oxides. In particular porous silicate materials comprise a large family of zeolites. Particularly suitable are various molecular sieves such as various natural molecular sieves: rhombosite, mordenite, erionite, faujasite, clinoptilolite and artificial zeolites of the A, X, Y, L, beta, and/or ZSM type. There are such a wide variety of zeolite structures that not all types can be mentioned here. Surprisingly, it has been found that effective thermal insulation of the mask can be achieved even in a thin layer applied to the shadow mask. Likewise, beneficial effects can be obtained when utilizing porous solid particles of phosphates such as the usual aluminophosphates, silicoaluminophosphates and metalloaluminophosphates, which can be produced synthetically and in small, medium, Classification by macropore type.

Other suitable porous solid particles are added clay minerals, layered phosphates and silica gels and the various known aluminosilicates.

In particular, electron-reflecting, electron-absorbing and heat-radiating covering layers combined with heat-insulating layers contain various heavy metal compounds, among which bismuth oxide and bismuth sulfide and lead oxide and lead sulfide, as well as tantalum oxide, cerium oxide and titanic acid are particularly suitable for use barium.

In particular, various crystalline and glassy silicates, phosphates and borates can be used as binders for coatings and thermal insulation, among them water glass and low melting glasses such as welding glasses and metal phosphates has been found to be useful. The various adhesives described above are characterized by high adhesive properties not only on the surface of the cover but also between the layers. This results in a coating with exceptional mechanical stability, further increasing the dimensional stability of the shadow mask.

The coating of the layer can be effected according to known coating methods, for example sputtering onto the surface of the hood and can thus be carried out at low cost.

When the average particle size is between 1 and 10 microns, the layer thickness of the thermal insulation layer is between 10 and 50 microns, while the heavy metal chalcogenide used usually has a thickness of 1.5 to 4.5 microns. Underneath the insulating layer, _the shadow mask may have a known blackened grayscale, for example composed of _Fe3O4 .

The advantage of the invention is that the arching of the iron hood is significantly improved, thus making it possible in many cases not to use expensive Invar alloys for the hood.

According to the shadow mask of the present invention, wherein the heavy metal compound is a black compound of a heavy metal or a mixture of heavy metals.

A shadow mask according to the invention wherein black and non-black heavy metal compounds are combined.

The shadow mask according to the present invention, wherein the surface of the covering layer is painted black.

According to the shadow mask of the present invention, wherein the heavy metal compound is barium, lead, titanium, bismuth, cerium, or tungsten compound.

The shadow mask according to the present invention, wherein the binder is a silicate or phosphate containing material.

A shadow mask according to the present invention, wherein said binder is a crystalline and/or glassy metal silicate, metal phosphate, metal borate and/or various glasses.

The present invention will be described in more detail below with reference to the accompanying drawings and several embodiments.

Description of drawings

Figure 1 is a color picture tube represented by a cross-sectional view;

Figure 2 shows the shadow mask in top view;

Figure 3 shows a shadow mask in cross-section;

Fig. 4 shows a cross-sectional view of the layer structure of the present invention.

FIG. 1 shows a color picture tube, the main part of which consists of a tube 1 with a fluorescent screen 2 and an electron beam system 7 arranged at the neck 5 of the tube. The phosphor screen 2 has on its inner side 3 a patterned luminescent layer which, as is known, produces an image when an electron beam strikes it. The conical portion 4 of the envelope 1 forms a funnel-shaped joint between the phosphor screen 2 and the neck. The neck 5 terminates in a socket 6 . The electron beam system 7 comprises a plurality of cathodes and other electrodes for generating and controlling the electron beam.

A shadow mask 8 is arranged on the inner surface 3 of the phosphor screen 2 by a mask frame not shown in the figure.

A high operating voltage of 25-30 kV is supplied via the anode contact 9 .

FIG. 2 shows a portion of the shadow mask 8 in plan view, where the shadow mask is indicated by 22 . The thickness of shadow mask 22 is typically from 0.130 to 0.280 millimeters within a narrow tolerance range. Chemically etch the desired pattern of holes.

The shadow mask 8 required for the function of the tube is formed by deep drawing.

In order to evaluate picture tubes which are under electron beam bombardment during operation, the impact behavior of electron beams is studied. For this, the maximum modulation area of the shadow mask 22 is used, which area is represented by four measurement points 25 , 24 , 26 , 27 . The deflection of the electron beam impingement due to the heating of the shield under electron beam bombardment is a criterion with regard to the quality of the picture tube and ultimately the success of the various measures taken to avoid arching in the picture tube.

The structure of the shadow mask 22 is shown in FIGS. 3 and 4 . Porous mask 22 formed with etched holes 33 has Fe ₃ O ₄ -blackened grayscale layer 36 . The cathode side is coated with a heat insulating layer 32 .

The thermal insulation layer 32 is covered with a covering layer 34 composed of heavy metal chalcogenides. Due to the structural design of the shadow mask 8, only a part of the electrons passes through the shadow mask 22 and reaches the emitter layer. A majority 38 of the electron beam strikes the shadow mask 22 . Due to the heavy metal atoms present in the blanket 34, a smaller portion 40 (approximately 30%) of the electron beam is reflected and other portions lose their energy in the blanket, thus heating the blanket. Thermal insulation layer 32 prevents heat transfer to steel shadow mask 22 . The heat is emitted to the rear side, ie in the direction of the electron beam system 7 .

The main component of the coating layer 34 is heavy metal chalcogenides with a particle size of less than 1 micron. The chalcogenide particles are fixed to the underlying insulating layer 32 using a conventional binder.

According to the invention, the insulating layer 32 is composed of porous solid particles, in this case the porous material consists essentially of the synthetic zeolite M _2/n O*Al ₂ O ₃ *xSiO ₂ *yH ₂ O, this zeolite It is an alkali metal-containing aluminosilicate (M = metal ion). For example a zeolite of structure type A has a modulus value x=2 and contains 2 parts of SiO ₂ and 1 part of Al ₂ O ₃ . The pore size in zeolite 4A is 0.4 nm and the volume of the pores is about 23%.

A zeolite sold under the trade name WESSALITH P by the company Degussa has been used with success. The particle size of the zeolite powder is between 0.5 and 9 microns at an average particle size _D50 of 3.5 microns. The particle size is further reduced by grinding.

The porous solid particles are fixed on the substrate by water glass glue. A good adhesion of the insulating layer 30 and the cover layer 34 can be achieved by using water glass as an adhesive, and by using additives such as surfactants and water, the wettability of the suspension can be adjusted before coating.

For applying the insulating layer 32 and for applying the cover layer 34, the sputtering method has proven to be a useful method.

Measurements of the service life of picture tubes carried out according to the invention show characteristics compared to picture tubes without an A/D layer. A comparison of the net deviation of a picture tube with an uncoated ferrous cover with that of a picture tube coated according to the invention shows that the net deviation can be significantly reduced for the coated cover. The pure deviation value for the uncoated mask is thus reduced to 50%. This _is also significantly better than the pure deviation of the hood coated with only _B2O3 (30%).

In each measurement, an electron beam at 270 microamperes and 24 kV was used to scan an area of 10 x 10 cm2 in the critical area of the picture tube, and the rest of the phosphor screen was not excited by the electron beam.

Detailed ways

Example 1

The cathode side of a _shadow mask consisting mainly of iron metal and having a blackened grayscale layer of _Fe3O4 on both sides is coated with an insulating layer and a cover layer using two consecutive sputtering operations.

Directly above the shield is a first insulating layer with a thickness of 20 micrometers, which is formed by sputtering a suspension consisting of 20 parts of zeolite 4A, Na ₁₂ [(AlO ₂ ) ₁₂ (SiO ₂ ) ₁₂ ]·12H ₂ O (average particle size is 2 microns), 5 parts of sodium silicate solution (5.8M; Na/Si=0.61; 0.1), 30 parts of water and 0.001 part of surfactant.

After drying the insulating layer in a stream of hot air, a covering layer of 3 µm thickness was formed on the insulating layer by sputtering a suspension composed of 2 parts bismuth oxide, Bi ₂ O ₃ (average particle size 0.9 µm) , 10 parts of sodium silicate solution (5.8M; Na/Si=0.61:1.0), 75 parts of water and 0.001 part of surfactant.

After sputter-coating the coating, the mask was baked at a temperature of 300°C.

Example 2

The composition of the suspension is the same as in Example 1, except that the insulating layer is formed by sputtering a suspension of the following composition: 20 parts of mesopored zirconium dioxide, ZrO ₂ (average particle size 2.5 microns), 4 parts Zirconium tetrapropoxide Zr(OH ₂ Cr) ₄ , 4 parts tetraethoxysilane (C ₂ H ₅ O) ₄ Si (alkali prehydrolyzed), 20 parts propanol C ₃ H ₇ OH, and 0.2 part water.

Example 3

The composition of the suspension is the same as in Example 1, except that the insulating layer is formed by sputtering a suspension of the following composition: 20 parts of microporous α-zirconium dihydrogen phosphate, α-Zr(HPO ₄ ) ₂ (using alumina Al ₂ O ₃ for heat stabilization), 2 parts of 80% phosphoric acid H ₃ PO ₄ , and 40 parts of water.

List of reference signs

1 Tube Shell 22 Shadow Mask

2 fluorescent screen 24 measuring points

3 inner side 25 measuring points

4 cones 26 measuring points

5 pipe neck 27 measuring points

6 Socket 32 Thermal Insulation

7 Electron Beam System 34 Covering Layer

8 shadow mask 36 Fe ₃ O ₄ blackened grayscale layer

9 Anode Contacts 38 Main Parts

40 smaller portions

Claims (14)

1. A shadow mask for a color picture tube, which is mainly composed of iron metal, the shadow mask is fixed with a frame, and the shadow mask is configured on the inner side of the fluorescent screen, the cathode side surface of the shadow mask has at least one layer of heat insulating layer and at least one heavy metal-containing cover layer, the heat insulating layer is disposed between the shadow mask and the cover layer, characterized in that the heat insulating layer is composed of thermally stable porous solid particles, and each layer contains a binder . 2. The shadow mask according to claim 1, wherein the porous solid particles are oxides or solid particles containing silicate or phosphate or a mixture of these solid particles. 3. The shadow mask according to claim 2, wherein the oxide solid particles are porous metal oxide particles comprising: titanium dioxide, zirconium dioxide and silicon dioxide. 4. The shadow mask of claim 2, wherein the silicate-containing solid particles are zeolite, columnar clay or silica gel. 5. The shadow mask of claim 2, wherein the phosphate solid particles are aluminophosphates, silicoaluminophosphates and metalloaluminophosphates and metallophosphates including zirconium phosphate. 6. The shadow mask of claim 1, wherein the cover layer is composed of a heavy metal compound and an adhesive. 7. The shadow mask according to claim 6, wherein the heavy metal compound is a heavy metal chalcogenide, a heavy metal nitride or a heavy metal carbide. 8. The shadow mask according to claim 7, wherein the heavy metal chalcogenide of the cover layer is an oxide or a sulfide. 9. The shadow mask according to claim 6, wherein the heavy metal compound is a black compound of a heavy metal or a mixture of heavy metals. 10. The shadow mask of claim 9, wherein black and non-black heavy metal compounds are combined. 11. The shadow mask of claim 1, wherein a surface of the covering layer is painted black. 12. The shadow mask according to claim 6, wherein the heavy metal compound is barium, lead, titanium, bismuth, cerium, or tungsten compound. 13. The shadow mask of claim 1, wherein the binder is a silicate or phosphate containing material. 14. The shadow mask of claim 1, wherein the binder is a crystalline and/or glassy metal silicate, metal phosphate, metal borate and/or various glasses.

Images